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,6. {Jaw Mai ATTORNEY Patented July 19, 1949 2,476,916 EiiECTRICRESISTANCE VACUUM FURNACE Herbert A. Rose, Forest Hills, and Dwight L.Hopl r, Wilkinsburg, Pa, house Electric Corporation, East Pittsburgh,

minors to Westinga corporation of Pennsylvania Application September 8,1945, Serial No. 815,172 19 Claims. (Ci. 13-31) Our invention isdirected to improvements in high temperature furnaces, and in turnacesysterns adapted to heat material to temperatures in the order of 2000C. and higher while in a rarified atmosphere having a pressure of as lowas fractions of 9. micron of mercury.

A primary object of our invention is to provide means for rapidlyremoving occluded gases from a material. Graphite anodes for use inhighpower mercury tube-rectifiers are examples of materials which can bedegassed in apparatus following the teachings of our invention, thedegassing being to an extent and at such speeds as all rarely attainedwith apparatus usedin prior practice.

An object of our invention is to provide a heatlug chamber in which allportions are at essem tielly the same high operating temperature.

An ancillary object of our invention is to provide a. high temperaturefurnace which is free from refractory and insulating ceramics so thatthe furnace can be satisfactorily used for de gassing without beingburdened with gases from materials ordinarily used in furnace construction.

Another ancillary object of our invention is to provide heating elementsupports which constitute part of the heating system and soar-ranged asto minimize heat losses from the furnace.

Another ancillary object of our invention is to provide a heatingresistor element which can eucompass a charge, the resistor elementbeing adapted to be heated to extremely high temperatures, but havingsuch a construction that it readily adapts itself to changes indimensions arising out of heating and cooling.

Another ancillary object of our invention is to provide a furnaceadapted to receive a vacuum pumping system, using an oil-diffusion pumpand means, specifically in the form of cooled baflles, for preventingback diffusion or migration of oil vapor into the furnace.

Another ancillary object of our invention is to provide a furnace inwhich the radiation shields are used to surround the charge-heatingspace in such a manner as to minimize heat losses and to make the use ofrefractory-tile insulating material unnecessary.

A preferred form of our invention comprises a lower region, whichreceives the charge to be treated, and a smaller upper region, whichcomprises a. gas chamber. The lower region includes electric heatingmeans surrounded by open radiation-shields which confine the heat sothat the or pumping system is connected to the exhaust gas from thefurnace, the connection being made at the gas chamber. The pumpin systemincludes an arrangement of diflerent pumps for quickly exhausting theinside of the furnace and quickly removing any gases which may be drivenfrom the furnace parts and from the charge when the furnace temperaturerises rapidly.

Other objects, innovations, features, combinatious and. methods of ourinvention, in addition to the foregoing, will be discernible from. thefollowing description of a preferred form thereof, which isto be takenin connection with the 3.0 companying drawing on difierent scales unlessotherwise specified.

In the drawings:

Figures 1a and lie, when placed with the form-er directly above thelatter and their lines il-ri fitting, constitute, to scale, a verticalview, partby in section and partly in. elevation with parts broken forclarity, of a furnace embodying the principles of our invention;

Fig. 2 is 2. sectional view on the line E-Li of Fig. lb and is drawn tothe same scale;

Fig. 3 is a diagrammatic view showing a vac uum pumping system attachedto the furnace shown in. Figs. 10. and 127;

Fig. d is a sectional view of a heating resistor element, as seensubstantially on the line Il -W of Fig. la;

Fig. 5 is a sectional view of a part of a co ductor-means through whichelectricity passes into the furnace for energizing its heating resistorelement; and

Figs. 6 and 7 are edgewise and broadside views, respectively, of abaiile means used in the pipe connection between the furnace and thevacuum pumping system.

The furnace shown in the drawings comprises an upright vacuum-tightmetallic furnace casing indicated in its entirety by the referencenumeral 2. The casing has an outer wall 4 comprising a hollow steelcylinder. Welded to the top and bottom portions of the cylinder aresteel annular members or rings 5 and 8, respectively, through which passspaced bolts l0 for receiving steel closures of the casing, comprising asteel top plate i2 and a steel bottom plate M. Vacuum-tight joints areprovided between the rings and the closures by means includingmetal-encased gaskets i5 protected from radiant heat by narrow rings I8secured to the inside of the cylindrical wall 4 near its edges.

Passing through the bottom plate H are a pinslze of the furnace can bekept down. A vacuum rality of water-cooled conductor-means, orconprotuberance 38 seating in a seat in the bottom plate, and an upperoutwardly-threaded stem 82. An inner pipe 34 is received inside theconducting rod 28 and terminates just short of the closed end of therod. An outlet pipe 36 and a seal 31 are provided near the bottom of theconducting rod 28. Cooling water delivered into the pipe 84 flowsupwardly through it, around its top open end and downwardly between thepipe and the inside wall of the conducting rod 28, and out through pipe86.

The conductor-means further comprises a graphite member 38 screwed onthe stem 22 or the conducting rod 28. This graphite member is also shownin Fig. 5. It has an upper hollow cylindrical portion 48 which snuglyreceives in it a similarly shaped lower portion 4! of a round graphiterod 42 of the conductor-means 28. The rod 42 extends upwardlyconsiderably beyond the graphitemember 38. The cylindrical portion 40has a longitudinal cut or slit 44 and a tapered outside thread 45 whichreceives a suitable graphite nut 46 so that the graphite member 88 andthe graphite rod 42 can be tightly clamped together to provide goodelectrical contact therebetween. The rod 42 comprises an upper portion58 of less diameter than the lower portion 4|, so as to provide acircular supportin shoulder 52. The top of the upper portion 50 isprovided with a threaded part 54 which extends upwardly from an uppershoulder 56. A terminal 58 is clamped around the conducting rod 28 belowthe bottom plate l4 or the casing 2.

Each of the conductor-means 22, 24 and 28 passes vacuum-tightly throughbut insulated irom the bottom plate l4. They are substantially alike sothat the following description of one should suflice for the three. Eachcomprises a round ceramic sleeve 60 of porcelain passing through a hole82 in the bottom plate [4. The sleeve has a top flange 64 supported,through a gasket 88, on a circular seat in the bottom plate l4. Anannular metal plate III, with an enlarged hole, bears on the top of theflange and compresses the gasket 66 by means of bolts 12 which arethreaded into holes in the bottom plate 14, spaced around the hole 62through which the sleeve 60 passes. metal-to-porcelain seal I4 isprovided between the sleeve 80 and the bottom of the bottom plate I4 fora further sealing of the hole 62. The sleeve 60 carries a metalconductor rod 16 -by means of a nut "threaded on the rod, and pressingon a spring 8|! which bears-on a washer 82 on an inside shoulder 84 ofthe sleeve 68. The nut forces a lower flange 86 of the conductor rod I8against a gasket 88 which bears against the bottom of the sleeve 60. Ametal-to-porcelain seal 90 further seals the space between the sleeve 60and the conductor rod I6. The conductor rod I6 is water-cooled throughan internal construction such as that provided for the conductor-means28.

Each insulated conductor-means also includes a graphite member 94threaded on the top of the conductor rod 16. and a graphite rod 96 whichis received in a split hollow upper cylindrical portion 98 of thegraphite member 94. A nut E00 on a tapered thread of the member 98tightly clamps the graphite member 94 around the lower end of thegraphite rod 96. Each conductor-means is further provided with aterminal l2 clamped around its conductor rod 16, below the sleeve 60.The graphite rod 96 of each insulated conductormeans 22, 24 and 26extends considerably above the top of the graphite rod 42 of theconductormeans 20.

In the particular embodiment of our invention which is herein shown anddescribed, the central conductor-means 28 is connected to one side orterminal of a power supply, and the insulated conductor-means, 22, 24and 26 are connected in parallel to the other side or terminal of thepower supply. Consequently, the insulated conductormeans aresubstantially at the same potential, and each carries about one-third ofthe current carried by the conductor-means 20, thereby limiting theheating of the metal-to-porcelain seals between the conductor-means andthe casing.

Connected between the central conductormeans 26 and the outer insulatedconductormeans 22, 24 and 26 is an electrical heating means which can beheated to temperatures as high as 2000 C. and above. This heating meansconsists of a resistor element which is so shaped that it can alsofunction to receive within it a charge to be heat-treated. A pluralityof spaced radiation-shields surrounds the resistor element for confiningthe heat. The resistor element and the shields are all of graphite andare free to expand and contract. These and the other graphite parts forthe furnace are preferably of that grade which can be machined and isstrong mechanically. Graphite known in the electrical art as rectifieror anode graphite is highly satisfactory.

The resistor heating element is in the form of a cup-shaped memberindicated in its entirety by the reference numeral 6. It comprises asubstantially solid relatively thick bottom wall 2 and an upwardlyextending thinner cylindrical wall I I4 to the outer upper end of whichis threaded a substantially solid thick annular graphite member or ring6, extending outwardly. The bottom 2 and the ring 6 comprise supportmembers or means by which the resistor element is supported. The bottomwall 2 is provided at its center with a threaded hole which receives thethreaded top part 54 of the conductor-means 20; and the ring 8 has threeequally spaced threaded holes which receive the tops of the insulatedconductor-means 22, 24 and 26, so that the resistor element is carriedand positioned by the different conductor-means. The ends of theconductor-means are flush with or below the surface of the members inwhich they are screwed.

The cylindrical wall 4 of the heating resistor element I I6 is providedwith a plurality of narrow 5 horizontal perforated rows havingrelatively long and narrow openings or grooves 8, each row comprisingfour equal openings of slightly less than 90 span, transverse to theaxis of the wall I I 4. The adjacent rows have their openingssymmetrically staggered, with the ends of each open- I openings in eachwall row, and narrow cylindrical rows I 22 between the perforated rows.Because of the openwork construction of the resistor element, currentflowing between the central conductor-means 20, on the one hand, and theconductor-means 22, 24 and 26, on the other hand, must zigzag throughthe cylindrical wall II4. Assuming that the current flows from thecentral conductor-means 20, it divides into paths as more or lessillustrated by the arrows shown in Fig. la, on the resistor element. Thecurrent-flow paths are considerably elongated and may be said tocomprise four parallel paths through the resistor element I I0, becauseof the four narrow separating walls I 20 between each narrow solidcylindrical portion I22 of the cylindrical wall II4. However, at the topof the resistor element, the solid ring II6 collects the current flowingfrom the wall H4, and the current divides so as to flow to the graphiterods 96 of the insulated conductormeans 22, 24 and 26. v

The resistor element can be electrically heated to incandescence so thatit radiates energy to any charge which is placed inside the resistorelement, the charge preferably resting on the bottom wall I I2 andclearing the cylindrical side wall II4.

In order to attain the desired high temperatures at satisfactoryefiiciency, heat losses from the resistor element must be minimized. Tothis end, the graphite rod 42, which carries the resistor element III],also supports on its shoulder 52, a plurality of disc-type horizontalradiation-shields I24, I26 and I28 held spaced by graphite spacers I30.Each of these disc-type radiation-shields has three outer holes throughwhich passes, with adequate clearance, the graphite rods 96 of theinsulated conductor-means 22, 24 and 26. The lower radiation-shield I24has a larger outer diameter than the others. Each of the top and bottomradiation shields I24 and I28, respectively, is thicker than either ofthe intermediate radiation-shields I26, for strength, and is providedwith an annular outside seat I32. The seats I32 receive and carryconcentric tubular radiation-shields I34. The top disc-typeradiation-shield I28 is also provided with a plurality of outerconcentric grooves between its rod-receiving holes. As shown in Fig. 2and by the dash lines at the upper left of Fig. 11), these groovesreceive groups of spaced arcuate partly-cylindrical uprightradiation-shields i136, a group being provided between each pair of rods96 but adequately spaced therefrom for electrical insulation. As shownin Fig. 2, the partlycylindrical radiation-shields H36 are spaced andlocked together by a plurality of spacers and pins Me at a plurality ofplaces in each group.

A plurality of additional upright outer cylin drical radiation-shieldsS42 are carried concentrically beyond the radiation-shields i34 by astep ring I 34 secured to the inside .of the casing i, as shown in Fig.lb.

A plurality of stacked spaced horizontal diselike radiation-shields 44Bare provided above the resistor element iii! and correspond in diameterto the outer diameter of the ring 3 id. The lowermost of these upperradiation-shields has a depending portion 548 loosely resting in agroove of the ring H6 and the others have spaced depending lugs 151iloosely resting on shoulders in the immediately lower radiation shield.These upper disc-like radiation-shields are obviously carried by theresistor element H0.

Central openings are provided in the upper radiation-shields I46 forfree gas passage and for observing the charge through a non-magnetic 6peep tube I62 in the top plate I2 01 the casing. This peep tube isgas-tightly covered with a replaceable glass plate I54, and has an innermetal sighting tube I56 closable by a pivoted iron cover I58 biased toclosing position, but movable to opening position by energization of anelectromagnet I60, which magnetizes a closure-attracting iron pole I62.

The metal furnace casing 2 is water-cooled wherever possible; and tothis end water-cooling coils I64 are wrapped around the cylindricalcas-- ing wall 4," and on the top and the bottom casing plates I2 and I4in any convenient manner, the tubing of the coils being flattenedagainst the members they are to cool for better thermal rela-- tiontherewith.

It may be observed from Figs. 1a and lb that a comparatively large gaschamber I66 is provided between the removable top plate I2 of the metalfurnace casing 2 and the uppermost part of the radiation shields. Avacuum pumping system is connected to this gas chamber for maintaining ahigh vacuum in the furnace. The vacuum pumping system is shownschematically in Fig. 3 as comprising a mechanical rotary vacuum pumpI68 having an intake comprising a pipe I10 secured to the furnace casing2, and opening at the gas chamber I66. A valve I12 is provided in thispipe and a by-pass system, including an oil diffusion pump I14 andvalves I16 and I18, branches around the valve I12. The portion of thepipe I10 near the furnace 2 is water-cooled by a coil I wrapped aroundit. Within the pipe I10, near the gas chamber I66 of the furnace, are aplurality of spaced staggered baffles I82 of coppper upon which any oilvapor diffusing backwardly from the vacuum pumping system condenses andthereby is prevented from contaminating the furnace graphite or chargeinside the furnace casing 2. Any convenient means may be provided fordraining the oil, if this is found to be necessary. Figs. 6 and 7illustrate a baffle. The baffle is built of two sections I84 and I88having partly-circular peripheries and pivoted at I88 so that they canbe spread tightly against the inside of the pipe I10 by means of aspreading mechanism I90. The peripheries of the baffie sections areprovided with metal braid M2 to assure adequate thermal contact betweenthe battle and the pipe.

In operation the furnace is loaded by first re moving the top plate I2and the upper radiation.- shields M6. The charge is placed inside the resister element I50. The radiation-shields we then can be replaced andthe top plate l2 securely bolted back on.

Electric power supplied to the resistor element l I G heats it toextremely high temperatures, driving out gas from the furnace parts andfrom the charge inside the resistor element. The gases are drawn intothe gas chamber by the vac uum pumping system, readily passing throughthe various openings in the resistor element and radiation-shields, andthrough the spaces between the radiation-shields. In operating tnevacuum pumping system, the valves H6 and 18 are first closed and thevalve I12 opened so that the rotary vacuum pump will operate to quicklyreduce the pressure in the furnace to a pressure of to 200 microns. Thevalve S12 is then closed and the valves E16 and I18 opened so that theoil diffusion pump I14 is added to bring the pressure down to fractionsof a micron. In a specific embodiment, a rotary vacuum pump with a speedof 300 c. f. m, and an eight-inch oil diffusion pump with a speed oi the600 c. f. m. brought the furnace pressure down to ten microns in lessthan a minute.

It should be noted that all the radiation-shields are comparativelyloosely supported. The conductor-means are secured only at the pointswhere, they pass through the bottom plate I4. The top of theconductor-means and the tops of the conductor-means 22, 24 and 26 areassociated with the resistor element III) which has considerable givebecause of its numerous long openings or slots H8. It acts in the natureof a bellows and readily accommodates itself to changes in dimensionsand locations arising out of high temperature variations duringoperation of the furnace. It easily follows changes in the lengths ofthe conductor-means and its own climensional changes without introducingshearing forces or other forces tending to disrupt the arrangement ofthe parts inside the furnace, or to break them. By having the variousconductormeans pass through the same end of the casing, the distancebetween their ends tends to remain more nearly the same with changes intheir lengths caused by heat.

An indication of the size of furnace of a specific embodiment such asherein described may be gathered from the fact that in this particularembodiment, the outside diameter of the steel cylindrical wall l or themetal casing 2 was 21% inches. The length between the facing surfaces ofthe top and bottom plates 6 and 8 was 51 inches. The resistor elementhad an outer diameter of close to 11 /2 inches at'its cylindrical wall IH and winner diameter of close to 10 inches.

While we have described our invention in a particular form nowpreferred, it is evident that many featuresof it are distinctly noveland subject towide modification, and that other forms embodying ourinvention will be apparent from the teachings herein described.

We claim as our invention:

1. A furnace'oi a type described comprising an outer metallic casinghaving a removable end, a heating resistor element of graphite insidesaid casing, said resistor element having an end and a tubular portionadapted to encompass a charge, said tubular portion having an open end,and having a plurality of relatively narrow and elongated staggeredtransverse openings throughout, a plurality of spaced radiation-shieldsaround said tubular portion, and a plurality of spaced disc-likeradiation-shields between said tubular portion and said removable end ofsaid casing, loosely fitted so as to be readily removable rom andinsertable into radiation-shielding position.

2. A furnace of a type described comprising an outer metallic casinghaving an end, a heating resistor element of graphite inside saidcasing, said resistor element having a charge-receiving end and atubular portion adapted to encompass a charge, said tubular portionhaving an open end, and having a plurality of relatively narrow andelongated staggered openings throughout, a first conductor-meanscomprising a graphite rod connected centrally to said charge-supportingend of said resistor element, and a plurality of spaced conductor-meanscomprising graphite rods connected to the opposite end of said resistorelement.

3. The invention of claim 2 characterized by said graphite rodsextending away from said resistor element, in the same direction, andsaid openings being transverse to the axis of said tubular portion.

4. A furnace of a type described comprising an outer metallic casinghaving an end, a heating I said tubular portion having an open end, and

having a plurality of relatively narrow and elongated staggeredtransverse openings, a first conductor connected centrally to said firstend of said resistor element, said resistor element having anoutwardly-extending ring spaced from first end, and conductor-meanssecured to spaced points of said ring.

5. The invention of claim 4 characterized by said conductor-meanscomprising graphite bars associated with said resistor element, saidgraph ite bars having end-portions carrying said resistor element, andadditional portions eaten in the same direction from said end portions.

6. A furnace adapted for degassing comprising an outer metallic casinghaving a removable end, a cup-shaped heating resistor of graphite insidesaid casing, said cup-shaped resistor having an end and anupwardly-extending tubular portion adapted to encompass a charge, saidtubular portion having an open end, and having a plurality of relativelynarrow and elongated staggered openings throughout, a plurality ofspaced curved radiation-shields around said tubular portion, and aplurality of spaced disc-like radiationshields at both ends of saidcup-shaped resistor element, the end radiation-shields toward saidremovable end of said casing being loosely fitted so as to readily beremovable from and insertable into radiation-shielding position, a firstdownwardly-directed conductor-means connected centrally to said bottomof said resistor element, an outwardly-extending ring at the upper endof said tubular portion, and downwardly-directed 4 conductor-meanssecured to spaced points of said annular ring, said conductor-meanspassing through and clearing said radiation-shields.

'7. A degassing furnace system comprising an outer upright vacuum tightmetallic casing having a removable top, a cup-shaped heating resistor ofgraphite having a bottom and an upwardly extending tubular portion forreceiving a charge, said tubular portion having a plurality ofrelatively narrow and elongated staggered openings throughout, a centralconductor-means vacuum-tightly passing through the bottom of saidcasing, a plurality of spaced disc-like radiation-shields of graphitecarried by said conductor-means below said resistor-bottom, a pluralityof radiation-shields comprising upright curved sections of graphiteloosely carried about said tubular portion of said resistor, and aplurality of spaced upper disc-like radiatiomshields of graphite looselycarried above said resistor element by said upright radiation-shields.

8. The invention of claim '7 characterized by said casing extendingabove said upper disc-like radiation-shields to provide a gas chamberthereabove, and a. vacuum pumping system connected to said gas chamber.

9. A high-temperature furnace of a type described adapted for degassingoperation, comprising an outer metallic casing, an expansiblecarbonaceous heating resistor element comprising a tubular portionproviding a charge-receiving space, said resistor element having an openupper end, outwardly directed support means at said upper end, and asupport member across its bottom end, a plurality of conductor meansincluding relatively insulated conductors vacuumtightly passingthrough-said casing, a. first of said conductors being under saidsupport member and comprising a carbonaceous portion extending to saidsupport member, said carbonaceous portion being electrically connectedto said support member centrally thereof, a plurality of spaceddisc-like carbonaceous radiation-shields under said support member, saidradiationshields being carried by said first conductor.

10. A high-temperature furnace of a type described adapted for degassingoperation, comprising an outer metallic casing, an expansiblecarbonaceous heating resistor element comprising a tubular portionproviding a charge-receiving space, said resistor element having an openupper end, outwardly directed support means at said upper end, and asupport member across the bottom end of the resistor element, and aplurality of conductor means including relatively insulated conductorsvacuum-tightly passing through said casing, a first of said conductorsbeing under said support member and comprising a carbonaceous portionextending to said support member, said carbonaceous portion beingelectrically connected to said support member centrally thereof, saidconductor means comprising a plurality of other conductors comprisingcarbonaceous portions electrically connected to said support means, thelast said carbonaceous portions being spaced from each other andparallel to the axis of said tubular portion.

11. An invention in accordance with claim but characterized further by aplurality of carbonaceous spaced disc-like radiation-shieldshorizontally under said support member, having aligned holes therein,certain of said conductors passing through said holes.

12. An invention comprising that of claim 10 but further characterizedby upright radiationshields comprising curved portions circumferentiallybetween said other conductors.

13. An invention including that of. claim 12 but further characterizedby having a plurality of spaced removable superimposed radiation-shieldshorizontally above said heating resistor element, and a plurality ofradiation-shields horizontally below said heating resistor element, saidradiation shields being carbonaceous.

14. A high-temperature furnace or" a type described adapted fordegassing operation, comprising an outer metallic casing having aremovable upper portion, a hollow graphite resistor inside said casinghaving an open upper end toward said removable casing-portion, saidresistor comprising a bottom member for supporting a charge inside saidresistor, said resistor being slotted, a plurality of spaced uprightradiation-shields around said resistor, a plurality of spaced disclikeradiation-shields at both ends of said resistor, the radiation-shieldstoward said removable casing-pcrtion being loosely superimposed so as tobe readily removable from and insertable into radiation-shieldingposition, and conductor means connected to said resistor for supplyingsaid resister with electrical energy, said conductor means passingthrough said casing at places outwardly of the space between saidremovable casing-portion and said removable radiation-shields.

15. A high-temperature furnace of a type described adapted for degassingoperation, comprising an outer metallic casing having a removable upperportion, a hollow graphite resistor inside said casing having an openupper end toward said removable casing-portion, a graphite member at thebottom of said resistor for supporting a charge inside said resistor,said resistor being slotted, a plurality of spaced uprightradiation-shields around said resistor, a. plurality of spaced disc-.

be readily removable from and insertable into radiation-shieldingposition, a central conductor means vacuum-tightly passing through thebottom of said casing, and electrically connected to said resistor, aplurality of spaced outer conductor means vacuum-tightly passing throughthe bottom of said casing and electrically connected to the top of saidresistor, said conductor-means being constructed and arranged forsupporting said resistor, said central conductor means and said outerconductor means being relatively insulated.

16. A high-temperature furnace of a type described comprising, an outermetal casing, a car-'- bonaceous heating element inside said casingadapted to receive a charge to be heated therein, said heating elementhaving a plurality of openings therethrough for increasing the path ofourrent-flow therethrough and for the passage of gas, said heatingelement being electrically insulated from said casing, and a pluralityof spaced carbonaceous radiation-shields substantially completely aboutall sides or said heating element, said radiation-shields being arrangedand spaced in said casing so as to permit gas to pass freely to and outof the spaces between them, and conductor means gas-tightly passingthrough said casing and connected to said heating element at spacedplaces thereon, said conductor means supporting said heating elementinside said radiationshields, said radiation-shields being so arrangedas to be electrically insulated from said heating element and saidconductor means so that the radiation-shields do not carry current.

17. A high-temperature furnace of a type described comprising, an outermetal casing, a carbonaceous heating element inside said casing adaptedto receive a charge to be heated therein, said heating element having aplurality of openings therethrough for increasing the path ofcurrent-flow therethrough and for the passage of gas, said heatingelement being electrically insulated from said casing, and a pluralityof spaced carbonaceous radiation-shields substantially completely aboutall sides of said heating element, said radiation-shields being arrangedand spaced in said casing so as to permit gas to pass freely to and outof the spaces between them, a first carbonaceous conductor passingthrough a hole in a side of said casing and connected to an end saidheating element, a second carbonaceous conductor passing through a holesaid side of said casing and connected to the opposite end of saidheating element, insulating vacuum-tight sealing means at said holesbetween said conduotors and said casing, said conductors supporting saidheating element and passing through spaces provided by a plurality ofsaid radiation-shields, out of electrical contact therewith.

18. A high-temperature furnace or" a type described adapted fordegassing operation, comprising an outer vacuum-tight metallic casing, acarbonaceous heating resistor element comprising a tubular portionproviding a heat-treating space, means connected to separated places onsaid tubular portion for passing electric current through it, saidtubular portion having elongated narrow passages therein, a plurality ofspaced 4'5 carbonaceous radiation-shields at all sides ofsaid element innon-current-carryingrelation thereto, said plurality ofradiation-shields bein constructed-and arranged to permit gas to pace efreely from the spaces therebetween and .irom the-space inside of theresistor element into the rest of the casing, relatively insulated.carbonarceous'conductors passing through said radiationshields-Iorsupplying said resistor element with electrical energy, saidconductors being spaceinsulated from said radiation-shields, said casing'plpe connection to said gas-chamber.

'19. An invention including that of claim 1% but further-characterizedby a plurality of said radiation-shields comprising removablesubstantiallyhorizcntal discs above said resistor element,

said gas-chamber being above said discs.

' HERBERT A. ROSE.

DWIGHT L. HOPE-m.

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